My feeling is that the pairing system as it stands is not really fit for purpose. I know this has been said before, but clearly the best way to do this is to have it like the ranking games whereby you are presented a map of guilds in and around your level and you choose and challenge them just like ranking games. The whole system could work exactly like ranking games in fact so it shouldn't be too much of a ball ache to code.

I get that incentivising people to build stadiums is important but there are better ways of doing that. Firstly people will do it anyway for the money - or simply to spend the money they have and have nothing left to spend it on. Secondly you could incentivise it by having a slight home advantage coded into the algorithm based on numbers of fans. Therefore, like in real rugby, it is slightly easier to win at home than away. It doesn't have to be a massive difference, just enough to make it just about noticeable. Maybe something equivalent to a match bonus of 1% perhaps for a fully maxed lvl 26 stadium? Arbitrary figure I know, but perhaps someone can suggest a better one.

These two things would radically change and improve the game in my opinion without being a huge amount of work for the developers.

Or perhaps the home advantage could be based on how many more fans you have than your opponent. If you have less fans than them, but the % is at a minimum and then have a sliding scale from there. Again, I think that's quite in line with real rugby.

You should take the guild ranking position of the guild you beat. If the draw was based on guilds ranked around your guilds position it wouldn't take too long for the rankings to sort themselves out and the strongest guilds be at the top and playing each other.

The trouble with picking your gc opponents is that they don't get a choice. When do they get to pick? You'd have to take in turns or have two gcs running (one you picked and people who picked you), it wont work that easily.
However I do like jungles idea of taking their rank when you beat them. It could be worked similarly to how it is allready except fans are only used to set your initial rank then it is down to gcs if you stay there. You'd have to have a higher ranked guild then a lower next to keep it fair (so yiu get a shot at improvement in rank then a defense of rank.) that's my 10p anyway.